Conventionally, for example, a damper is provided in an assist grip and the like which is an interior of an automobile, and brakes a movement when the assist grip returns to an original position by a restoring force of a spring and the like. As for such a damper, for example, there are a damper device described in Patent document 1 described hereinafter, and a method for manufacturing a resin molded member including an undercut portion described in Patent Document 2 described hereinafter.
In the damper device described in Patent Document 1, a cylindrical inner part which is a rotor, and a cylindrical outer part which is a housing are concentrically integrated. Each part is integrated by fitting an annular projection formed on an outer periphery of the inner part into an annular groove formed on an inner periphery of the outer part. The projection and the groove in molding are generally so-called undercuts, respectively.
On the other hand, in the method for manufacturing the resin molded member including the undercut portion described in Patent Document 2, a resin molded member is made by an inner slide forming die and an outer slide forming die. In the inner slide forming die, there is formed an annular projection for forming an annular groove on an inner periphery of the resin molded member, wherein a taper enlarging in diameter in a direction of being removed from the resin molded member is made. When the inner slide forming die is removed from the resin molded member, the projection can easily slip out of the groove of the resin molded member by the taper.